(a) Field of the Invention
The present invention relates to a split combo bearing. More particularly, the present invention relates to a split combo bearing including a thrust bearing and a radial bearing.
(b) Description of the Related Art
In parts (rotor shaft and moving shaft) that make motions such as rotation or reciprocation, various types of bearings are provided to solve problems such as wear or damage of the parts, noise, and waste of energy due to friction that may be generated in the motions of the parts. The bearing on which loads are applied perpendicular to the rotational axis is called a radial bearing or a journal bearing (for sliding bearings) and the bearing on which loads are applied in parallel with the rotational axis (that is, axially) is called a thrust bearing. Most bearings called thrust bearings and rolling bearings are classified into a thrust bearing on which axial loads are applied at over 45 degrees and a radial bearing in the other cases.
A technology regarding a radial bearing is disclosed in International Patent Publication No. 2010-122450 (“A MAGNETIC BEARING, A ROTARY STAGE, AND A REFLECTIVE ELECTRON BEAM LITHOGRAPHY APPARATUS”, 2010.10.28), and a technology regarding a thrust bearing is disclosed in U.S. Patent Publication No. 2009-0039740 (“Magnetic Bearing”, 2009 Feb. 12).
Further, recently, a divisional type of power generation technology has been increasingly commercialized all over the world due to an increase in costs for initial installations because the cost per kilowatt for transmitting power is consumed in a large amount in centralized systems, and there is a need for inexpensive basic structures that are installed to distribute generated power to consumers. With this tendency, micro gas turbines that are small gas turbines capable of generating power directly at the sites are increasingly used. Micro gas turbines or micro turbines, which are small-sized gas turbines, generally have output of less than 1 kW or of hundreds of watts. Those micro gas turbines are being increasingly developed and used for divisional types of power and small-scaled cogeneration systems because of technical advantages and the environmentally-friendly characteristic.
It has been known that the rotor shafts of the small devices such as the micro gas turbines usually rotate at high speeds of 10,000˜400,000 rpm in order to achieve desired output. Radial bearings and thrust bearings are necessary for the small devices as well. In particular, for small high-speed rotors such as the micro gas turbine of which the necessity and the actual use are increasing, there is an increasing need of bearings that can be reduced in size and weight, satisfying the conditions of non-contact type and no oil supply, in addition to the conditions required for bearings, that is, reduction of axial vibration, usability under high-temperature environments, and high durability.
In general, the bearing systems of rotors are composed of a radial bearing that supports radial loads and a thrust bearing that supports axial loads, as described above. However, there is a problem in that the bearing systems on rotors necessarily increase in volume, because the bearings are all separate parts. The larger the volume of bearing systems, the larger the length of rotors becomes, and accordingly, the primary bending mode (critical speed) of the rotors lowers, which causes a problem in that the stability of small rotors is considerably decreased in high-speed rotation.
Further, in the process of separately manufacturing the two types of bearings and assembling them, a specific back plate on a rotor for the thrust bearing is needed and there is a need for a process for meeting the degree of precision in assembling, thereby causing the assembly process to be complicated.
Further, since it is required to install a thrust collar for using a thrust bearing on a rotor, for a high-speed rotor in a small system, when the system is complicated, a bending mode frequency is reduced by a thrust collar and it causes a problem in rotating the rotor at the ultra-high speed.
Further, the following problems have been generated with the progress of studies for improving the shapes of small rotors such as those used in the micro gas turbines described above. FIG. 1 is a view showing the configuration of bearings on a rotor shaft assembled with an impeller in the related art. In the related art, a turbine impeller t and a compressor impeller c are separately assembled on a rotor shaft s. That is, the impellers t and c are assembled on an end portion of the rotor shaft s and then fixed by bolts and nuts. In order to assemble the assembly of the rotor shaft and the impellers with a common bearing, the bearing b can be installed while the impellers t and c are installed on the rotor shaft s.
However, in the rotor having this configuration, assembling the high speed rotor shaft with the parts has caused problems such as a high imbalance and low bending mode. As a way of solving the high imbalance and low bending mode during high-speed rotation, a technology for manufacturing a rotor shaft and impellers in one unit, breaking away from the method of separately manufacturing a rotor shaft, a compressor impeller, and a turbine impeller and then assembling them, has been studied in recent years. However, in spite of the design and development of an impeller-rotor shaft-integrated rotor to overcome the problem of high imbalance that is generated when a rotor shaft and impellers are assembled, there is another problem in that it is very difficult to install the bearings of the related art with the impeller-rotor shaft-integrated rotor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.